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 01/21/97 3:43pm
Reply to message #113 from Robert Astalos: > Reply to message #101
from Lars Holmstrom: > > Following an example straight out of a >
> Mathematica supplement for an Engineering > > Mathematics book,
I get the wrong output > > than I should: > > > > In[1]:= <<Calculus`VectorAnalysis`
> > > > In[2]:= F = {7 x, 0, -z} > > > > Out[2]= {7 x, 0, -z} > >
> > In[3]:= Div[F] > > > > Out[3]= 0 > > > > The result should be
6, as it says in the > > book. I also get the result of 0 using >
> the Grad[] and Curl[] functions, no matter > > what they are acting
on. Any ideas? > > > > Sorry I missed this the first time! If you
type > > In[2] := ??Cartesian > > Mathematica will tell you that the
default coordinate variables are > Xx, Yy, Zz. If you do > > In[3]
:= Div[ {7 Xx, 0, -Zz} ] > > you will get the right answer. When I
looked in my copy of ''Guide to > Standard Mathematica Packages'', it
sure looks like the variables are > x, y, z, but then my copy is Version
2.2. I assume that this was > changed for 3.0. > > Robert > ___________________________________________________________________________
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There has indeed been a change in the default Cartesian coordinates
in Version 3.0: ----- Version 2.2 ----- In[1]:= <<Calculus`VectorAnalysis`
In[2]:= Div[ {7 x, 0, -z} ] Out[2]= 6 In[3]:= ?x {x,y,z} are the default
Cartesian coordinates. ----- Version 3.0 ----- In[1]:= <<Calculus`VectorAnalysis`
In[2]:= Div[ {7 Xx, 0, -Zz} ] Out[2]= 6 In[3]:= ?Xx ''{Xx,Yy,Zz} are
the default Cartesian coordinates.'' In[7]:= ?x ''Global`x'' My guess
is that this change was made to accomodate the use of x as a common
user defined symbol. Tom Zeller Forum Moderator ___________________________________________________________________________
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